In a packet transmission network having a current-use packet transmission path and a spare packet transmission path used when a fault has occurred, a technique is needed in which the packet transmission network is recovered from the fault, by switching the packet transmission path at high speed without imposing a load on the packet transmission network when the fault has occurred, in order to maintain the reliability of the packet transmission network.
As the recovery method in the packet transmission network, a linear fault recovery method is described in ITU-T G. 8032 recommendation (Non-Patent Literature 1). As the linear fault recovery method, there are a fault detection/switching and collecting method and a fault detection/switching and separating method. In the fault detection/switching and collecting method, a termination node in the packet transmission path carries out fault detection and recovery at the same time. In the fault detection/switching and separating method, a node which relays a packet on the packet transmission path detects a fault, transmits a fault notice to a termination node of the packet transmission path, and the termination node receiving the fault notice switches the packet transmission path. Generally, the fault detection/switching and separating method is used.
As an example of the conventional technique, the fault detection/switching and separating method will be described. FIG. 1 is a block diagram showing a packet transmission network 100 of the fault detection/switching and separating method in the conventional technique. The packet transmission network is configured of a node 11 to a node 18. The node 11 and the node 12 are connected through the node 17, and a current-use packet transmission path 110 is set therebetween. Also, the node 11 and the node 12 are connected through the node 16, and a spare packet transmission path 120 to the current-use packet transmission path 110 is set therebetween. The node 13 and the node 14 are directly connected, and a current-use packet transmission path 111 is set therebetween. Also, the node 13 and the node 14 are connected through the node 16, and a spare packet transmission path 121 to the current-use packet transmission path 111 is set therebetween.
When there is not a fault in the packet transmission network 100, the packet transmission is performed by using the current-use packet transmission path 110, and the current-use packet transmission path 111. Each node transmits a continuity check message (CCM) to a neighbor node regularly. Each node manages the activeness or inactiveness of the neighbor node by receiving the CCM regularly.
The case where the fault has occurred in the packet transmission network 100 will be described. It is assumed that a fault has occurred between the node 12 and the node 17. Because the node 12 does not receive the CCM from the node 17, the node 12 detects that the fault has occurred between the node 12 and the node 17. Similarly, because the node 17 does not receive the CCM from the node 12, the node 17 detects that the fault has occurred between the node 12 and the node 17. The node 17 outputs a fault notice data to the node 11 as a termination node of the packet transmission path 110, to indicate that the fault has occurred. The node 11 receives the fault notice data, and the node 12 detects the fault in the current-use packet path 110 by not receiving the CCM from the node 17. The node 12 switches the transmission path to the spare packet transmission path 120 from the current-use packet transmission path 110. In this way, the fault recovery is realized in the packet transmission path.
Next, in the packet transmission network 100, the internal configuration of the node of the fault detection/switching and separating method in the conventional technique will be described. Because the internal configurations of the node 11 to the node 18 are identical to each other, only the node 11 will be described.
FIG. 2A and FIG. 2B are block diagrams showing the configuration of the node 11 in the packet transmission network 100 of FIG. 1. The node 11 is provided with a line card 201-1, a line card 201-2 and a packet switch 230. Because the internal configurations of the line card 201-1 and the line card 201-2 are identical, only the internal configuration of the line card 201-1 will be described.
The line card 201-1 is provided with an external reception section 210-1, an internal transferring section 211-1, an internal reception section 212-1, an external transferring sections 213-1, FDB (transferring database) 214-1, a current-use/spare path switching section 215-1 and a path unit fault notifying section 216-1.
The external reception section 210-1 is provided with a packet receiving section 217-1 and a fault detecting section 218-1. The internal transferring section 211-1 is provided with a multiplexing section 219-1 and a packet transferring section 220-1. The internal reception section 212-1 is provided with a packet receiving section 221-1 and a fault notice data processing section 222-1. The external transferring section 213-1 is provided with a packet transferring section 223-1.
The FDB 214-1 is a table which retains destination data necessary to transfer a packet when transferring the packet, such as a MAC address of a next destination node, and the number of a port connected to a network to which the destination node of the packet is connected.
The current-use/the spare path switching section 215-1 refers to the FDB 214-1 to transfer the reception packet to the next destination node. The packet received from which of the current-use packet transmission path and the spare packet transmission path should be transferred is determined by the fault notice data processing section 222-1 notifying to the current-use/spare path switching section 215-1.
The path unit fault notifying section 216-1 specifies the packet transmission path passing through a faulty section by referring to the FDB 214-1, and generates the fault notice data in units of the packet transmission paths. The path unit fault notifying section 216-1 transfers the fault notice data to the multiplexing section 219-1.
The packet receiving section 217-1 of the node 11 receives the packet transmitted to a port of the line card 201-1 connected to the neighbor node of the node 11
The fault detecting section 218-1 confirms whether a CCM is received from the node connected to the port of the line card 201-1. When the reception of the CCM within a constant time cannot be confirmed, the fault detecting section 218-1 detects that the fault has occurred, and transmits a fault detection notice to the path unit fault notifying section 216-1. The fault detecting section 218-1 transfers a packet except for the CCM to the current-use/spare path switching section 215-1.
The multiplexing section 219-1 multiplexes the packets transferred from the current-use/spare path switching section 215-1 and the path unit fault notifying section 216-1.
The packet transferring section 220-1 transfers the packet which is received from the line card 201-1, toward the line card with a port connected with the next destination the node.
The packet receiving section 221-1 receives the packet from a port of any of the line cards of the nodes 11 through packet switch 230.
The fault notice data processing section 222-1 refers to the received fault notice data and the FDB 214-1 to determine the packet transmission path to be switched, and instructs the current-use/spare path switching section 215-1 to switch the path from the current-use packet transmission path to the spare packet transmission path.
The packet transferring section 223-1 transfers the packet from the port connected with the next destination node which neighbors the node 11.
The packet switch 230 in the node 11 transfers the packet which is received from the port of any of the line cards to the port of the line card which is connected with the destination node.
In the fault detection/switching and separating method of the conventional technique, when a fault has occurred among the nodes for the packet transmission path, a termination node of the packet transmission path generates the fault notice data which contains data for specifying the packet transmission path in which the fault has occurred. The fault notice data unicasted for the termination node of the packet transmission path. The termination node receiving the fault notice data switches the packet transmission path from the current-use packet transmission path to the spare packet transmission path. At that time, there sometimes is a site where the fault has occurred between the nodes of the spare packet transmission path after the switching. In this case, once again, the fault notice data is transmitted to the termination node of the packet transmission path after the switching, and the packet transmission path is switched once again. In this way, in the fault detection/switching and separating method of the conventional technique, when the fault has occurred simultaneously at a plurality of sites, it is assumed to successively switch the packet transmission path, and there is possibility that switching time has been extended.